(In reply to comment #5)
> (In reply to comment #4)
> > I'm also seeing something else waiting for vsync. With glReadPixels() out of
> > the picture, and glXSwapIntervalMESA(0), I'm still getting 60 fps and no
> > tearing. Possibly related?
> 
> Either
> 
>  Option "SwapbuffersWait" "off"
> 
> and/or
> 
>  Option "EnablePageFlip" "off"
> 
> should avoid that.

I see. In the interest of being honest to applications, shouldn't
glXGetSwapIntervalMESA() return 1 when those settings are on?